1. Field of the Invention
This invention relates to nanocomposite semiconductor materials and structures for applications in various electronic, optoelectronic, photonic and plasmonic devices, such as inorganic or organic semiconductor materials incorporating aligned nanowires made of metals or semiconductors. It describes a fabrication method employing new process of photo-modification for self-assembling the aligned nanowires and nanowire arrays made of metal or semiconductor materials at specific positions in the near-surface region or in bulk of the matrix semiconductor material, which are defined by light illumination. It also provides examples of some new optoelectronic and photonic components, which could benefit from application of the developed technology and nanocomposite materials. Preferred embodiments include components of diffractive optics, diffraction gratings, phase retardation plates and polarizers operating in both visible and infrared spectral regions, antireflection layers, all-optical and electro-optical spatial light modulators, nonlinear optics and optical limiters, linear and nonlinear waveguide components for optical signal processing, Bragg gratings, photonic crystals, optical recording of information, infrared detectors, light emitting diodes and diode lasers.
2. Background of the Invention
Metal or semiconductor nanowires are building blocks of many future nanodevices. Semiconductor materials are workhorse of the most current and future optoelectronic and photonic devices. Therefore methods for fabricating the nanocomposite semiconductor materials comprising aligned arrays of nanowires are fundamentally important for development of many electronic, optoelectronic, photonic and plasmonic devices.
There are many methods for fabrication of nanowires employing different growth mechanisms. The method of vapor-liquid-solid (VLS) [Wu Y, Yang P. J Am Chem Soc; 123 (2001) 3165-66] enables controlled growth of the one-dimensional nanostructures with the assistance of metal catalysts prepared from particles or thin films. After injecting precursor gases, semiconductor wires grow from the catalytic particles at an elevated temperature [Hamilton, J. M., Romano, L. T.: WO06016914A2 (2006).]. However, the metal catalysts contaminate the grown nanowires and complicate the nanowire fabrication process. An extra purification is required for removing the catalysts. Therefore, one of the major challenges in fabricating nanowires is to synthesize high purity single-crystalline nanowires without using metals catalysts in the process.
The nanowire-like semiconductor crystals can be fabricated using colloidal methods patented by Alivisatos et al. [Alivisatos, A. P., Peng, X., Manna; Liberato: US20016225198 (2001)]. By using mixtures of surfactants that bind to different crystallographic faces, the shape of growing crystals could be controlled. To control the growth directions of nanocrystals one can adjust the ratio of organic surfactants changing the surface energies of the growing crystal faces.
Nanowires can also be fabricated using electrodeposition, where metal nanowires are grown on a template containing nanometer-sized cylindrical pores in a suitable insulating membrane having one side coated with a metal layer as an electrode. Chien et al. patented an invention [Chien, C. L., Searson, P. C., Liu, K.: U.S. Pat. No. 6,187,165 (1998)] on the fabrication of bismuth nanowires by using this method. After inserting the coated membrane into a suitable deposition solution containing a bismuth-based electrode as the second electrode, bismuth nanowires can be obtained by applying a voltage. The diameter of the wires can be controlled from tens of nanometers to microns depending on the pore size.
Another patent related to the template growth of nanowires employs asymmetric lattice-mismatch between two crystalline materials [Chen, Y., Williams, S. R., Ohlberg, D. A. A.: US20036656573 (2003)]. This allows epitaxial growth of the self-assembled nanowires on a crystalline substrate. The nanowires can be aligned on the surface due to preferential growth in one direction. The self-assembled nanowires are only formed with an appropriate deposition rate and deposition temperature.
The present invention is related to the method of fabrication of aligned metal or semiconductor nanowires incorporated into a matrix semiconductor material employing new process of photo-modification of the semiconductor materials. The nanowires and nanowire arrays are self-assembled in the light illuminated regions of semiconductor from charged interstitial defect atoms, which are ether inherently present in the semiconductor material or artificially introduced in this material. The nanocomposite materials comprising the aligned arrays of nanowires incorporated in the semiconductor material find numerous applications in various electronic, optoelectronic, photonic, and plasmonic devices, some of which are described in this patent.